Explaining the MiniBooNE Anomalous Excess via Leptophilic ALP-Sterile Neutrino Coupling

Abstract: Recently, the MiniBooNE experiment at Fermilab has updated the results with increased data and reported an excess of $560.6 \pm 119.6$ electronlike events ($4.7\sigma$) in the neutrino operation mode. In this paper, we propose a scenario to account for the excess where a Dirac-type sterile neutrino, produced by a charged kaon decay through the neutrino mixing, decays into a leptophilic axionlike particle ($\ell$ALP) and a muon neutrino. The electron-positron pairs produced from the $\ell$ALP decays can be interpreted as electronlike events provided that their opening angle is sufficiently small. In our framework, we consider the $\ell$ALP with a mass $m^{}_a = 20\,\text{MeV}$ and an inverse decay constant $c^{}_e/f^{}_a = 10^{-2}\,\text{GeV}^{-1}$, allowed by the astrophysical and experimental constraints. Then, after integrating the predicted angular or visible energy spectra of the $\ell$ALP to obtain the total excess event number, we find that our scenario with sterile neutrino masses within $150\,\text{MeV}\lesssim m^{}_N \lesssim 380 \,\text{MeV}$ ($150\,\text{MeV}\lesssim m^{}_N \lesssim 180 \,\text{MeV}$) and neutrino mixing parameters between $10^{-10} \lesssim |U_{\mu 4}|^2 \lesssim 10^{-8}$ ($3\times 10^{-7} \lesssim |U_{\mu 4}|^2 \lesssim 8 \times10^{-7}$) can explain the MiniBooNE data.